This invention relates in general to a containment device and in particular to a containment device for retaining semiconductor wafers that provide for automated loading and unloading of the semiconductor wafers therein while minimizing the breakage of the semiconductor wafers during loading, unloading and transporting.
Without limiting the scope of the present invention, its background will be described with reference to transporting semiconductor wafers from one site to another.
Heretofore in this field, it has been necessary to transport semiconductor wafers from one fabricating facility to another between certain steps in the fabrication process. The process for packaging the semiconductor wafers for transport was typically a manual process which required placing each of the semiconductor wafers into individual electrostatic discharge bags in order to prevent the buildup of static charge on the semiconductor wafer that may otherwise occur during handling. The static charge must be prevented in order to avoid causing short circuits within the semiconductor wafer.
Once the semiconductor wafers were placed into electrostatic discharge bags, the semiconductor wafers were placed into a styrofoam box. The styrofoam box was typically treated with a topical anti-static coating such as Staticide made by ACL Corporation or other quaternary compounds. The use of the topical anti-static coating on the styrofoam box further prevented the buildup of static charge during handling of the semiconductor wafers.
It has been found, however, that the use of styrofoam boxes can promote the corrosion of semiconductor wafers due to the potential moisture retention by the styrofoam. The typical process used to mold the styrofoam box is a steam process wherein beads of styrofoam are exposed to steam which causes them to expand and allows them to be formed into the shape of a box. If the styrofoam boxes are not properly dried, the residual moisture within the styrofoam box may cause corrosion of the semiconductor wafers.
The use of styrofoam boxes also left semiconductor wafers susceptible to breakage. For example, it is estimated that between one and three percent of semiconductor wafers were broken during the manual loading and unloading process as well as during transportation of the semiconductor wafers in the styrofoam box. In addition, the use of styrofoam boxes to transport silicon wafers resulted in high costs associated with the manufacture and disposal of the styrofoam boxes which, in most cases, were not re-used or recycled.
Therefore, a need has arisen for a containment device for retaining semiconductor wafers that will allow for automated loading and unloading of semiconductor wafers, thereby minimizing the breakage of semiconductor wafers associated with the transportation of semiconductor wafers from one facility to another. A need has also arisen for such a containment device that dissipates static charge without the need to manually place the semiconductor wafers within an electrostatic discharge bag. A need has further arisen for a containment device for retaining semiconductor wafers that does not promote corrosion of the semiconductor wafers. Additionally, a need has arisen for such a containment device that is re-usable, thereby minimizing both the manufacturing and disposal costs associated with transporting semiconductor wafers.
The present invention disclosed herein comprises a containment device for retaining semiconductor wafers that provides for automated loading and unloading of the semiconductor wafers therein while minimizing the breakage of the semiconductor wafers during loading, unloading and transporting. The containment device of the present invention dissipates static electricity through the use of electrically conductive materials and does not promote corrosion of the semiconductor wafers as the materials used do not retain moisture. Additionally, the containment device of the present invention is reusable, thereby reducing both the manufacturing and environmental costs associated with transporting semiconductor wafers.
The containment device in accordance with a first embodiment of the present invention comprises a first housing member having a frame, an inner wall and an outer wall. The inner and outer walls extend generally perpendicularly from the frame and have a spaced apart relationship forming a gap therebetween, the inner wall closely spaced from the semiconductor wafers when receiving the semiconductor wafers to prevent radial movement of the semiconductor wafer during transportation. The containment device also includes a second housing member that is securably attachable to the first housing member. The second housing member has a frame that forms the top of the containment device when the first and second housing members are securably attached together.
The inner and outer walls of the containment device each have a slot that allows for automated loading and unloading of semiconductor wafers. In addition, the inner wall has a notch for establishing the maximum depth of semiconductor wafers to be retained within the containment device. Both the frame of the first housing member and the frame of the second housing member may include reinforcement members for minimizing flexure of the containment device during transportation. The second housing member may further include a wall that extends generally perpendicularly from the frame of the second housing member that is disposed exteriorly of the outer wall of the first housing member when the first and second housing members are securably attached together. The frame of the second housing member may also include a spacer member that minimizes the axial movement of the semiconductor wafers within the containment device when the first and second housing members are securably attached together.
The first housing member and the second housing member are securably attached together using one or more latches that are hingably mounted to the first housing member. In first embodiments, each latch is attached to the first housing member and has a hook that is received and secured within a hole in the frame of the second housing member. The latches and holes receiving the latches are preferably positioned 180 degrees apart when two such latches are used and 90 degrees apart when four such latches are used, ot being understood that the number of latches used can be any number greater than one. The use of, for example, four spaced apart latches as compared to two spaced apart latches provides for greater flattnes of the housing as the housing diameters increase, such as, for example up to 300 mm. The latches are disposed at corners or sides of the housing with the corners being preferred, especially when the housing is the preferred rectangular (square) shape, it being understood that the housing can have other shapes, such as, for example circular. Once the first housing member and the second housing member are securably attached together, similar containment devices may be stacked one on top of another using the respective lips of the first housing members and the second housing members. In accordance with a second embodiment, a rotatable flap is secured to the first housing member and has a hook on the distal end thereof for overlapping the second housing member and entering an aperture on the top of the second housing member to provide the latching action. A plurality of such rotatable flaps are used, the embodiment shown having two such flaps, it being understood that additional such flaps can also be provided in spaced relation in the same manner as discussed above with reference to the first embodiments.
Prior to loading the containment device with semiconductor wafers in accordance with the first embodiments, a cushion is placed in the bottom of the first housing member. A wafer separator is then place on top of the cushion. Thereafter, numerous semiconductor wafers are place within the containment device and closely received within the inner wall of the first housing member using an automated process. This process includes placing a wafer separator between each semiconductor wafer. Once the level of the semiconductor wafers reaches the notch of the inner wall of the first housing member, a cushion is placed on top of the last semiconductor wafer with a wafer separator therebetween. The second housing member may then be securely attached to the first housing member.
The materials selected for the containment device of the present invention must not only protect the semiconductor wafers from impacts or shocks to the exterior of the containment device but must also protect the semiconductor wafers from the ubiquitous build up of internal static. Specifically, the first and second housing members are constructed from a conductive material such as a carbon impregnated polypropylene. Similarly, the wafer separators are constructed from a conductive material which may be a carbon impregnated polyethylene. Additionally, the cushions used above and below the stack of semiconductor wafers may be constructed from an anti-static foam.
In accordance with the second embodiment of the invention, the outer wall is not provided and, instead, the remaining wall, which corresponds to the inner wall of the first embodiments, is lined with a very soft rubber or foam or the like, preferably of an antistatic variety, such as pink polyethylene antistatic foam, which will absorb shock applied to the housing. This embodiment provides added shock protection and becomes more useful as the diameters of the wafers increase and/or as the thicknesses of the wafers decrease.